Surge arresters are used to limit dangerous surges in electrical lines or devices. Gas-filled surge arresters are often used to protect small devices. A gas-filled surge arrester is usually composed of a small tube made of ceramic material which is closed off in an air-tight fashion at each of its open ends by an electrode. There is a noble gas in the interior of the small ceramic tube. The noble gas constitutes a high resistance when a voltage below a threshold value is present between the electrodes of the arrester, with the result that no current flows through the arrester. If the voltage which is present at the electrodes exceeds the level of a trigger voltage, the resistance of the arrester drops to very low values within microseconds. In the triggered state of the arrester, current peaks up to several kiloamperes are able to be diverted.
After the triggering of the arrester, a current flows between the two electrodes through the noble gas atmosphere in the interior of the arrester. The time when the arrester triggers is defined by the type of noble gas, by the pressure of the gas and the distance between the electrodes. Owing to the high current flowing through the arrester, heating occurs at the arrester in the triggered state. When a driving voltage which is present at the arrester decreases again below the level of the arc voltage or when current flowing through the arrester drops below a specific level again, the arrester is switched off and the internal resistance resumes its original operating state with several 100 MΩ.
However, under certain electrical conditions surge arresters cannot return to the non-conductive state again after they have been triggered. This situation occurs, for example, when a voltage above the trigger voltage is continuously present between the electrodes of the arrester. The current with a high current level which then flows through the arrester over a relatively long time can result in the arrester and its surroundings heating up to a great extent. If the arrester is not switched off in good time, it can finally become so hot that it is destroyed or its surroundings, for example on a circuit board are heated up so strongly than the components located in the surroundings are destroyed. In the case of extreme heating, the surroundings of the arrester can even catch fire. In order to avoid this, it must be ensured that the surge arrester switches off in good time, with the result overheating of the arrester and its surroundings can be prevented.